This invention relates to a method for determining the urea concentration in liquids as well as a urea sensor for carrying out the method.
The determination of the urea concentration is important, for instance, to kidney disease patients. For decontaminating the blood of these persons, i.e., for removing the urea from the blood, three methods are presently in use: hemodialysis, hemofiltration and peritonic dialysis. It is attempted here to free the urea containing electrolytes or blood filtrates which accumulate in these treatment methods, i.e., in the blood purification, of urea, so that the dialysis and substitution solutions which have been necessary heretofore, can be dispensed with. Then, however, it is of interest to see the result of the treatment and to indicate its end point, which necessitates an exact urea analysis.
Besides the methods mentioned above which have already been introduced, new methods for the elimination of urea are also being worked out such as electro adsorption or the so-called indirect urea oxidation. In this method also, it is necessary, however, to monitor the urea concentration, which requires reliable urea sensors.
It would also be of advantage if implantable urea sensors were available, because then the urea concentration in the blood of kidney disease patients could be monitored. A signal could then be released if a limit was reached and blood purification would be carried out.
Also for patients who suffer from diabetes, an exact urea determination would turn out to be advantageous. For, these persons could be helped with an implantable insulin dosing device, where a glucose sensor would make a control loop possible. However, the calibration curves of glucose sensors have so far been impaired by urea and therefore, an improvement could be achieved by a urea determination, i.e., the interference effect could be corrected.
Up to now, the urea content in (body) fluids has usually been determined intermittently by chemical analysis. Such a procedure, however, is unsatisfactory. While the urea concentration can also be determined continuously by means of an enzymatic sensor, the application is limited by the useful life of the enzyme membrane, and implantation is not possible.
It is an object of the present invention to provide a method for determining the urea concentration in liquids, which operates continuously, is sensitive, and permits a reliable determination of the urea content over long periods of time also.